Alistair M. Stephen

Food Polysaccharides and Their Applications

Introduction, Alistair M. Stephen and Shirley C. Churms Starch: Structure, Analysis, and Application, Henry F. Zobel and Alistair M. Stephen Modified Starches, Otto B. Wurzburg Starch Hydrolysates, Paul H. Blanchard and Frances R. Katz Cellulose and Cellulose Derivatives, Donald G. Coffey, David A. Bell, and Alan Henderson Galactomannans and Other Cell Wall Storage Polysaccharides in Seeds, Michael J. Gidley and J.S. Grant Reid Agars, Norman F. Stanley Gelling Carrageenans, Lennart Piculell Alginates, Kurt Ingar Draget, Storker T. Moe, Gudmund Skjak-Braek, and Olav Smidsrod Inulin, Anne Franck Pectins: Structure, Functionality, and Uses, J.A. Lopes da Silva, and M.A. Rao Bacterial Polysaccharides, V.J. Morris Gums and Mucilages, Peter A. Williams, Glyn O. Phillips, Alistair M. Stephen, and Shirley C. Churms Chitosans, Kjell M. Varum and Olav Smidsrod Polysaccharides in Food Emulsions, George A. van Aken Polysaccharide Rheology and In-Mouth Perception, K. Nishinari Phase Behavior in Mixed Polysaccharide Systems, Vladimir Tolstoguzov Dietary Fiber, Andrew Chesson Genetic Engineering and Food Crops, Jennifer A. Thomson Detection and Determination of Polysaccharides in Foods, Yolanda Brummer and Steve W. Cui Index

Some new aspects of the molecular structure of Acacia senegal gum (gum arabic)

Abstract The gum polysaccharide of Acacia senegal, the main source of gum arabic, has been re-examined by means of two series of sequential Smith degradations, one starting with the whole polysaccharide, the other with a product from which all acid-labile side-chains had been removed by prior partial hydrolysis. Investigation, mainly by methylation analysis and estimation of molecular weight, of the products obtained at each stage of these two series of degradations, both of which ultimately yielded small galactans that appeared to be identical, has afforded evidence for the presence in the polysaccharide chain of uniform blocks of (1→3)-linked d -galactopyranosyl residues; these blocks are comparable in size to those postulated for many arabinogalactans of simpler structure. Some amplification of the structural model proposed for this polysaccharide by earlier workers is possible in the light of these new data.

Fine structure of the arabinogalactan-protein from Lolium multiflorum

Abstract The extracellular arabinogalactan-protein from suspension-cultured cells of Lolium multiflorum (ryegrass) was purified in a single step by affinity chromatography of the culture medium on myeloma protein J539-Sepharose. The product obtained after two Smith-degradations had an apparent molecular size corresponding to that of galactoheptaose and was mainly (1→3)-linked. The Smith-degradation products were essentially monodisperse with respect to molecular size, indicating that periodate-oxidisable residues were distributed regularly along the polysaccharide chains. The polysaccharide chains in the arabinogalactan-protein were probably attached to hydroxyprolyl residues of the protein core via O -glycosylic linkages. No carbohydrate appears to be linked to serine or threonine residues. No oligo-arabinosides linked to hydroxyproline could be detected.

Spectroscopic and molecular comparisons of three fractions from Acacia senegal gum

Abstract The gum fractions isolated from Acacia senegal gum using hydrophobic affinity chromatography have been further characterized by 1 H- and 13 C-NMR spectroscopy and by methylation analysis. Fractions 1 and 2 are essentially polysaccharides of similar sugar and uronic acid content, the units of which have now been found to be linked in the same manner, despite a difference in the proportion of associated protein (0.44 and 9.18% respectively). The glycoprotein fraction 3 (carbohydrate content 50–54%), comprising a minor but important part of the whole gum, is made up of monosaccharide units in the same relative proportions, which are linked in a similar manner to those found for the major, carbohydrate-rich components. A molecular model proposed earlier, wherein five carbohydrate blocks such as make up fraction 1 are joined to polypeptide to form fraction 2, gains support from the near identity of the carbohydrate moieties in these fractions. The carbohydrate in fraction 3 is of lower molecular weight than that of 1, and may be attached to any of the hydroxy-amino acids present in abundance.

Carbohydrate polymers from Aloe ferox leaves

Abstract Leaves from Aloe ferox , divided mechanically into outer and inner layers, of which the outer formed the bulk, were extracted with organic solvents, and the residues were fractionated using in succession, water, aqueous ammonium oxalate, and alkalies of increasing concentration. Polysaccharide components were characterized by determining sugar composition and the modes of linkage of the constituent monosaccharide and uronic acid units. The bulk of the extracted carbohydrate was made up of arabinogalactan and rhamnogalacturonan, components of the inner and outer parts of the leaf differing little from one another.

Structural studies of an arabinogalactan-protein from the gum exudate of Acacia robusta

The gum exudate from Acacia robusta (subspecies clavigera) has been found to contain protein (18% w/w), bound to an arabinogalactan having structural features typical of the gum polysaccharides from Acacias of Benthams Series 4 (Gummiferae), of which A. robusta is a member. Three sequential Smith degradations yielded an oligosaccharide of molecular weight ∼700, indicating the presence in the galactan core of very small blocks of contiguous (1→3)-linked d-galactopyranosyl residues. Such an oligosaccharide was produced after only one Smith degradation, following removal of the l-arabinosyl units (constituting ∼50% of the total carbohydrate) by partial hydrolysis of the arabinogalactan with acid. This partial hydrolysis resulted in the detachment of a small proportion (∼25%) of the protein from the polysaccharide, whereas virtually all of it was detached by Smith degradation. These results have implications with regard to the nature of the linkages between the arabinogalactan and the 4-hydroxy-l-proline-rich, protein component of this gum.

Structural investigations of two capsular polysaccharides from cryptococcus neoformans

Abstract Two capsular polysaccharides from Cryptococcus neoformans serotype A have been shown to be chemically equivalent. One of these polysaccharides was further investigated and shown to consist of a chain of (1→3)-linked d -mannosyl residues, each of which is substituted at O–2 by a d -glucosyluronic acid or d -xylosyl group.

Structural features of the gum exudates from some Acacia species of the series Phyllodineae and Botryocephalae

Abstract Smith degradation of each of the polydisperse, gum polysaccharides from Acacia pycnantha, A. difformis, A. filicifolia , and A. podalyriaefolia , for which molecular-weight distributions have been measured by gel-permeation chromatography, gives, in good yield, a methanol-insoluble polysaccharide that shows a single peak on examination by this technique. The molecular weights of the Smith-degraded polysaccharides are close to the values expected if the respective gum polysaccharides, on losing periodate-vulnerable, peripheral sugar residues were to be split also at regular intervals between the otherwise (1→3)-linked d -galactose chains. The structures of these gums, which are similar in many respects, conform to the pattern shown recently to occur in the gum of A. baileyana .

Strucrural investigation of Klebsiella serotype K7 polysaccharide

Abstract Methylation analysis of and partial hydrolysis studies on the Klebsiella K7 capsular polysaccharide and its carboxyl-reduced derivative indicated the recurrence of D -glucopyranuronic acid, D -mannopyranose, and D -glucopyranose residues, linearly linked in a specific manner, in the molecular structure. D -Galactopyranose and pyruvic acid residues are linked to the main chain on the D -mannose residues (at O-3) and the D -glucose residues (at O-4 and O-6), respectively; the simplest interpretation of this evidence is that nine sugar residues and pyruvic acid constitute a repeating unit. The sequence →3)-β- D -GlcA p -(1→2)-α- D -Man p -(1→2)-α- D -Man p -(1→3)- D -Glc p → was demonstrated by the isolation from the polysaccharide of an aldotetraouronic acid of this structure.

The gum exudate of Encephalartos longifolius lehm. (female) (family cycadaceae)

Abstract The structural components of a polysaccharide gum from Encephalartos longifolius, earlier characterised by isolating the monosaccharides released on graded hydrolysis and by g.l.c. assay of the methanolysis products from the methylated polysaccharide, has been submitted to further acid hydrolysis in order to identify the acidic components and the sugars linked thereto. The biouronic acids 6-O-(4-O-methyl-β- d -glucopyranosyluronic acid)- d -galactose, 6-O-(β- d -glucopyranosyluronic acid)- d -galactose, and 2-O-(β- d -glucopyranosyluronic acid)- d -mannose, thus isolated, together with what appears to be a linear series of 2-O-(β- d -glucopyranosyluronic acid)- d -mannose polymers linked through C-4 of the d -glucuronic acid residues, constitute a high proportion of the total polysaccharide. This evidence, taken with the methylation data, is used to describe the structural units and their methods of linkage in the complex polysaccharide material.